1. Field of the Invention
The present invention relates to video signal recording apparatus for use with a video tape recorder (VTR) and, more particularly, to a video signal recording apparatus for down-converting and recording a chroma component.
2. Description of the Prior Art
In home VTRs, a chroma component included in a video signal is down-converted and the chroma signal thus down-converted is recorded together with a frequency-modulated (FM) luminance signal. In this case, the chroma signal is down-converted into a chroma signal having a frequency of 700 kHz, for example and a band width of this down-converted chroma signal lies in a range of from about .+-.400 to 500 kHz. The down-converted chroma signal having a relatively narrow band is recorded on a video tape together with the frequency-modulated luminance signal, whereby the video signal can be efficiently recorded on the video tape and a video system suitable for home use in which a tape consumed amount is limited can be constructed.
However, when the chroma signal is down-converted and then recorded on the video tape, there is then the disadvantage that the chroma component of the reproduced signal is deteriorated. That is, since the chroma signal is recorded such that the band width thereof is reduced by the above down-converting processing, it is difficult to restore the band width of the original chroma signal. Therefore, as compared with the luminance signal recorded according to the frequency modulation, the chroma signal is very poor from a characteristics standpoint.
In the real reproduced picture, the characteristic of the luminance signal is dominant apparently and the frequency characteristics of the luminance signal has been improved (high band) recently in order to improve the picture quality. In order to improve the picture quality more, it is requested to improve the characteristics of the chroma signal (i.e., improvement of color reproducibility).
To improve the chroma signal characteristic, it is proposed to shift a down-converting carrier of about 700 kHz to a slightly higher frequency by shifting the converting frequency to the high frequency side. If the down-converting carrier is varied as described above, however, a compatibility with the conventional VTRs is lost. Furthermore, if the down-converting carrier is set to a too high frequency, the frequency band of the down-converted chroma signal overlaps the recording band of the luminance signal recorded according to the frequency modulation. Therefore, the sufficiently high carrier cannot be set in actual practice so that a wholesale improvement of characteristics cannot be expected without regard for the problem of compatibility.
As a method in which characteristics can be improved only by the circuits on the playback side without changing the down-converted carrier, there is known a method which emphasizes the edge of the reproduced chroma signal. According to the edge improvement mentioned above, the characteristics are partly improved and a recording band cannot be enlarged fundamentally. Also, there is the disadvantage that a S/N (signal-to-noise) ratio is deteriorated.
FIG. 1 of the accompanying drawings shows an example of a conventional VTR 1.
As shown in FIG. 1, a video signal SV is supplied to an AGC (automatic gain control) circuit 2, in which it is corrected in signal level. The signal thus corrected from the AGC circuit 2 is supplied to a Y/C separating circuit 3, in which it is separated to provide a luminance signal Y and a chroma signal C.
Further, in the VTR 1, while the luminance signal Y is frequency-modulated to a recording signal YFM by a luminance signal processing circuit 4, the chroma signal C is supplied through a bandpass filter (BPF) circuit 5 to an ACC (automatic chroma level control) circuit 6, in which it is corrected in signal level and then fed to an emphasizing circuit 7.
Thus, in the VTR 1, the chroma signal is emphasized by the emphasizing circuit 7 and then down-converted by a converting circuit 8.
Further, in the VTR 1, the down-converted chroma signal is supplied through a low-pass filter (LPF) circuit 9 to an adding circuit 10, in which it is added with a tracking control pilot signal ATF and the recording signal YFM.
Further, in the VTR 1, an output signal from the adding circuit 10 is supplied through an amplifying circuit 11 to a magnetic head 12, whereby recording tracks are sequentially formed on a magnetic tape 13, thereby recording a video signal on the above recording tracks.
Whereas, in the reproducing system, an output signal from the magnetic head 12 is amplified by an amplifying circuit 14 and then a luminance signal is demodulated by a luminance signal processing circuit 15.
In the VTR 1, a chroma signal component is extracted from the output signal of the amplifying circuit 14 by a low-pass filter (LPF) circuit 16 and then corrected in phase characteristic. Then, this chroma signal component is corrected in signal level by an ACC circuit 17.
Further, in the VTR 1, the output signal from the ACC circuit 17 is supplied to a converting circuit 18, in which it is converted into a signal of the original frequency band. Then, this signal is sequentially supplied through a band-pass filter (BPF) circuit 19 and a comb filter circuit 20 to a de-emphasizing circuit 21.
In the VTR 1, the chroma signal is de-emphasized and then added with the luminance signal by an adder circuit 22, whereby the video signal SV is output through the adder circuit 22.
In this kind of VTR, the picture quality is improved by enlarging the frequency band of the luminance signal. Therefore, it is considered that, if the frequency band of the chroma signal is enlarged, then the picture quality can be improved more.
In this case, in the luminance signal recorded on the magnetic tape at its high band side, the frequency band can be enlarged comparatively easily while maintaining a compatibility with the conventional format. Whereas, the chroma signal is recorded on the magnetic tape at its low band side and the frequency band thereof is limited so that the frequency band cannot be substantially enlarged while maintaining the compatibility with the conventional format.